Subclinical infection with the nematode Trichostrongylus colubriformis increases gastrointestinal tract leucine metabolism and reduces availability of leucine for other tissues

Haemonchus contortus alters distribution and utilization of protein and amino acids in different tissues of host sheep

The objective was to determine host animal protein/amino acid redistribution and use among the abomasum, duodenum and muscle of sheep infected with Haemonchus contortus. Sixteen male Ujumqin sheep (32.4 ± 3.9 kg) were dewormed and randomly assigned to two groups, infected or not infected with H. contortus (GIN and CON). The GIN group had lower (P < 0.05) dry matter intake, average daily gain, and live body weight than CON, with extensive focal infiltration of lymphocytes in the lamina propria and bottom of the abomasal epithelium. In the abomasum and duodenum, there were 100 and 220 genes, respectively, that were up-regulated, whereas 56 and 149 were down-regulated. In the abomasum, the most enriched KEGG pathways were related to immunity and inflammation reaction, including: viral protein interaction with cytokine and cytokine receptor (P = 0.017), influenza A (P = 0.030), IL-17 signaling pathway (P = 0.030). In the duodenum, KEGG pathways were more enriched in nutrient metabolism, including pancreatic secretion (P < 0.001), protein digestion and absorption (P < 0.001), graft-versus-host disease (P = 0.004). Furthermore, most genes related with the above KEGG pathways were increased in the abomasum but decreased in the duodenum. Amino acid profiles in abomasum and duodenum of CON and GIN groups were clustered in a partial least-squares discriminant analysis model, with significant changes in 36 and 19 metabolites in abomasal and duodenal chyme, respectively. Further confirmed by transcriptome-targeted metabolome association analysis, GIN mainly enhanced metabolism of arginine and sulphur amino acids in abomasum and those metabolic pathways were associated. Meanwhile, GIN mainly decreased pyruvate related amino acid metabolism in duodenum. Moreover, concentrations of Arg (P = 0.036), His (P = 0.027), and Cys (P = 0.046) in longissimus thoracis et lumborum were decreased in GIN, whereas concentrations of Gly (P = 0.012) and Ala (P = 0.046) were increased. In conclusion, H. contortus enhanced metabolism of arginine and sulphur amino acids in the abomasum; decreased pyruvate metabolism in the duodenum; and drove more protein/amino acids for abomasal tissues to resist physical and immune damage, reducing protein and amino acids in duodenum and muscle for support host growth. Specific nutrients (such like arginine, histidine, and cysteine) may play important role in control gastrointestinal nematode infection for ruminant.

Influence of targeted selective anthelmintic treatment on the productive performance of wool and hair lambs naturally infected with gastrointestinal nematodes in Brazil

Targeted selective treatment (TST) is an alternative method to reduce the use of anthelmintics and delay the development of resistant nematode populations. However, there is limited information on the actual effects of this type of treatment on livestock productivity. The objective of this study was to evaluate the production performance of Santa Ines (hair) and Ile de France (wool) lambs naturally infected with gastrointestinal nematodes (GIN) under TST based on packed cell volume (PCV) versus suppressive anthelmintic treatments. Thirty-eight lambs were divided into two treatment groups: Suppressive treatment, animals were drenched with monepantel every two weeks and TST, animals were treated with the same anthelmintic when they presented PCV ≤ 20%. Feces, blood, and weight were measured weekly to determine eggs per gram of feces, PCV, total plasma protein, and weight gain. After animals were slaughtered, carcasses were weighed to determine carcass yield. In the TST group, substantial productive losses of approximately 21.3% in the wool and 25.9% in the hair lambs were observed in body weight compared to their counterparts. Significant differences in hematological variables occurred over the experimental period, especially in the wool lambs under TST. Favorable environmental conditions enabled infective larvae to survive and thrive on pasture. Haemonchus contortus and intestinal nematodes were the most common parasites found in the Ile de France lambs and the Santa Ines lambs, respectively. Although TST prevented mortality, it did not prevent production losses. Both breeds showed a significant drop in production due to GIN parasitism.

Trichostrongylus colubriformis infection damages intestine brush board cells and could negatively impact postabsorptive parameters of Santa Ines lambs

This study aimed to evaluate histological, digestive and postabsorptive physiological parameters in Santa Ines lambs infected with Trichostrongylus colubriformis and fed different levels of phosphorus. Therefore, eighteen Santa Ines, castrated male, six-month old, healthy lambs (initial body weight 22.4 ± 2.7 kg) were distributed in one of four treatments arranged in a 2 × 2 split-plot arrangement: Sufficient dietary P level and uninfected (SPui; n = 4), Sufficient dietary P level and infected (SPi; n = 5), Deficient dietary P level and uninfected (DPui; n = 4), Deficient dietary P level and infected (DPi; n = 5). Infected lambs received, orally, a single pulse dose of 40.000 T. colubriformis infective larval stage (L3). Animals were fed Tifton 85 hay (Cynodon ssp.; 60%), and cassava meal and maize gluten meal (40%). Measurement of nutrient apparent digestibility and nitrogen metabolism were performed in individual metabolic stalls. To achieve the trial results, it was measured methane emissions in respiratory chambers, urine purine derivatives, ruminal short-chain fatty acids (SCFA), histological cuts of duodenal mucosal tissues and passage rates fluxes, analyzed by external (Yb, Cr, and Co) and internal (iNDF) markers. Statistical procedures were performed in R studio. The fixed main effects of treatment and the interactions were tested by ANOVA, and means compared by Duncan's test at 5% significance. Apparent digestibility was not affected by treatments, however, nitrogen retained decreased (P < 0.01) and urinary nitrogen losses increased (P < 0.01) in infected animals. Small intestine digesta content, empty segment weight, and length were higher in infected animals (P < 0.05). Passage rate was not majorly affected by infection or dietary P levels. Methane emissions, SCFA concentrations, and purine derivative excretion were also not affected by treatments. Regarding the histology, the vilosity weight (P < 0.05), and crypt depth (P < 0.01) decreased in infected animals. In conclusion, T. colubriformis infection can damage intestinal mucosa and affect nitrogen metabolism, but did not affect the digesta transit, and nutrient digestibility. The P dietary levels did not promote any modification in GIT physiological parameters tested in this study.

Health Monitoring for Laboratory Salamanders

Laboratory animal health monitoring programs are necessary to protect animal health and welfare, the validity of experimental data, and human health against zoonotic infections. Health monitoring programs should be designed based on a risk assessment and knowledge about the biology and transmission of salamander pathogens. Both traditional and molecular diagnostic platforms are available for salamanders, and they provide complementary information. A comprehensive approach to health monitoring leverages the advantages of multiple platforms to provide a more complete picture of colony health and pathogen status. This chapter presents key considerations in the design and implementation of a colony health monitoring program for laboratory salamanders, including protocols for necropsy and sample collection.

Haemonchus contortus Infection Alters Gastrointestinal Microbial Community Composition, Protein Digestion and Amino Acid Allocations in Lambs

The objective of this study was to investigate associations between gastrointestinal microbiota and protein metabolism of lambs infected with Haemonchus contortus. Sixteen male Ujumqin lambs (initial body weight = 32.4 ± 3.9 kg) were dewormed and randomly assigned to 2 equal groups, to be infected or not infected with Haemonchus contortus (GIN and CON, respectively). The experiment lasted 77 days. The GIN lambs had lower packed cell volume (PCV) and increased wormegg count (WEC) after 14 days. Furthermore, in infected lambs, there were decreases in apparent digestibility of dry matter (P = 0.011), crude protein (P = 0.004) and ether extract (P = 0.007), as well as decreased ruminal pepsin (P < 0.001) and lipase (P = 0.032) activity but increased ruminal α-amylase (P = 0.004) and cellulase activity (P = 0.002), and decreased jejunal α-amylase activity (P = 0.033). In addition, infection with H. contortus decreased alpha diversity of the gastrointestinal microbial community in the rumen, abomasum and duodenum, although microbiota associated with carbohydrate and proteolytic metabolism were increased and up to 32 KEGG pathways in the duodenum were predicted to be significantly affected. In conclusion, H. contortus infection in lambs altered the gastrointestinal microbial community composition and disturbed protein digestion and allocation of absorbed amino acids. These results provided insights into consequences of H. contortus infection in lambs and could facilitate development of novel nutritional strategies to improve animal health.

Amino Acids in the Nutrition and Production of Sheep and Goats

In sheep and goats, amino acid nutrition is essential for the maintenance of health and productivity. In this review, we analysed literature, mostly from the past two decades, focusing on assessment of amino acid requirements, especially on the balance of amino acid profiles between ruminal microbial protein and animal production protein (foetal growth, body weight gain, milk and wool). Our aim was to identify amino acids that might limit genetic potential for production. We propose that much attention should be paid to amino acid nutrition of individuals with greater abilities to produce meat, milk or wool, or to nourish large litters. Moreover, research is warranted to identify interactions among amino acids, particularly these amino acids that can send positive and negative signals at the same time.

Tannin supplementation modulates the composition and function of ruminal microbiome in lambs infected with gastrointestinal nematodes

This study was carried out to evaluate the effects of tannin supplementation on ruminal microbiota of sixteen lambs infected and non-infected with Haemonchus contortus and Trichostrongylus colubriformis. Animals were fed with hay, concentrate and supplemented with Acacia mearnsii (A. mearnsii). The animals were divided into four treatments: two control groups without infection, either receiving A. mearnsii (C+) or not (C-), and two infected groups, one with A. mearnsii (I+) and another without A. mearnsii (I-). Ruminal short-chain fatty acids (SCFA) and metagenome sequencing of ruminal microbiota were used to evaluate the effect of tannin and infection on ruminal microbiome. For SCFA, differences were observed only with A. mearnsii. Total SCFA and acetate molar percentage were decreased in C+ and I+ (P<0.05). Butyrate, valerate and isovalerate were higher in lambs that received A. mearnsii in the diet (P<0.05). The infection changed the microbiome structure and decreased the abundance of butyrate-producing microorganisms. In addition, A. mearnsii supplementation also affected the structure the microbial community, increasing the diversity and abundance of the butyrate-producing and probiotics bacteria, amino acid metabolic pathways, purine, pyrimidine and sphingolipid metabolism. Together, our findings indicate that A. mearnsii supplementation modulates important groups related to nitrogen, amino acid, purine and pyrimidine metabolism, in rumen microbiome, affected by gastrointestinal nematodes infection in lambs.

Invited review: Nitrogen in ruminant nutrition: A review of measurement techniques

Nitrogen is a component of essential nutrients critical for the productivity of ruminants. If excreted in excess, N is also an important environmental pollutant contributing to acid deposition, eutrophication, human respiratory problems, and climate change. The complex microbial metabolic activity in the rumen and the effect on subsequent processes in the intestines and body tissues make the study of N metabolism in ruminants challenging compared with nonruminants. Therefore, using accurate and precise measurement techniques is imperative for obtaining reliable experimental results on N utilization by ruminants and evaluating the environmental impacts of N emission mitigation techniques. Changeover design experiments are as suitable as continuous ones for studying protein metabolism in ruminant animals, except when changes in body weight or carryover effects due to treatment are expected. Adaptation following a dietary change should be allowed for at least 2 (preferably 3) wk, and extended adaptation periods may be required if body pools can temporarily supply the nutrients studied. Dietary protein degradability in the rumen and intestines are feed characteristics determining the primary AA available to the host animal. They can be estimated using in situ, in vitro, or in vivo techniques with each having inherent advantages and disadvantages. Accurate, precise, and inexpensive laboratory assays for feed protein availability are still needed. Techniques used for direct determination of rumen microbial protein synthesis are laborious and expensive, and data variability can be unacceptably large; indirect approaches have not shown the level of accuracy required for widespread adoption. Techniques for studying postruminal digestion and absorption of nitrogenous compounds, urea recycling, and mammary AA metabolism are also laborious, expensive (especially the methods that use isotopes), and results can be variable, especially the methods based on measurements of digesta or blood flow. Volatile loss of N from feces and particularly urine can be substantial during collection, processing, and analysis of excreta, compromising the accuracy of measurements of total-tract N digestion and body N balance. In studying ruminant N metabolism, nutritionists should consider the longer term fate of manure N as well. Various techniques used to determine the effects of animal nutrition on total N, ammonia- or nitrous oxide-emitting potentials, as well as plant fertilizer value, of manure are available. Overall, methods to study ruminant N metabolism have been developed over 150 yr of animal nutrition research, but many of them are laborious and impractical for application on a large number of animals. The increasing environmental concerns associated with livestock production systems necessitate more accurate and reliable methods to determine manure N emissions in the context of feed composition and ruminant N metabolism.

Impact of gastrointestinal parasitism on dry matter intake and live weight gain of lambs: A meta-analysis to estimate the metabolic cost of gastrointestinal nematodes

This study aimed to estimate the effect of gastrointestinal nematodes (GIN) on the productive performance assessed by the live-weight change (LWC) of lambs, and the metabolic cost associated with parasitism by means of a meta-analysis. Data used in the meta-analyses were obtained from twenty papers selected using the following criteria: (a) lambs with (I) and without (NI) GIN; (b) lambs fed ad libitum; (c) LWC data; (d) feed consumption data; and (e) chemical composition of diets. The effect of diet composition (crude protein [CP] and metabolizable energy [ME]) on dry matter intake (DMI), and the effect of composition and nutrient intake (DMI and CP intake [CPI]) and ME intake (MEI) on LWC was evaluated using respective regression analyses. The metabolic cost of worm burden was determined as the difference in CP and ME requirements between NI and I lambs for each adult parasite. The CP and ME cost were evaluated for lambs at two different levels: maintenance level 0 g LWC and 100 g LWC. The worm burden had an impact on the DMI and LWC of lambs (P < 0.05). The association of CP x infection level was the best predictor of DMI. The association between MEI and infection level were the best predictors of LWC. The metabolic cost of GIN increased to 0.30 mg CP/kg LW^0.75 and 0.0056 kJ ME/kg LW^0.75 for each adult parasite. The metabolic cost was not modified by diet quality (maintenance level 0 g LW/day or 100 g LW/day). In conclusion, GIN has a negative effect on DMI and LWC. The metabolic cost of GIN infection can be covered by supplying the additional requirements for protein and energy in the diet of infected lambs.

Effect of dietary dry matter intake on endogenous nitrogen flows in growing lambs

The effect of dietary dry matter intake (DMI) on endogenous nitrogen (N) flows at different part of the digestive tract of growing lambs was determined using a ¹⁵ N isotope dilution technique. Three Kazakh male lambs (30 ± 2.75 kg of body weights and 4 months old, average daily gain 200 g/day) were fitted with ruminal, duodenal and ileal cannulae and raised in metabolic cage individually. The experiment was conducted in a 3 × 3 Latin square design with three lambs, three DMI levels (1100, 920 and 736 g/day respectively) and three periods. Each period lasted 18 days, consisting of 10 days for adaptation, 8 days for the continuous infusion of l-[¹⁵ N]leucine, during which the intestinal flow of N and ¹⁵ N enrichment were determined. The total endogenous secretions in the forestomach (S_fs ) were decreased (p = 0.0512) with increased level of DMI. On the contrary, endogenous nitrogen (EN) secretions into the small intestine (S_i ) increased (p = 0.0249) significantly with the high level of DMI (HI) group compared with that of low level of DMI (LI). Total absorption from forestomach was reduced (p = 0.0121) with increased level of DMI, whereas total absorption from small intestine for HI group increased (p = 0.0116) significantly compared with that of LI treatment. The real digestibility of N in the rumen accompanied with the increase in feed intake is decreased (p = 0.081). In contrast, there were no effects of DMI level on the computed real digestibility of N across both small intestine and whole tract. The results of this study indicate that the total flows of EN at duodenum may be unaffected by the level of DMI; however, the EN flow at ileal level increased from 12% to 37% with the increase in DMI level, corresponding to 33% of total N flow at ileum.

Whole-body and splanchnic amino acid metabolism in sheep during an acute endotoxin challenge

Supplemented protein or specific amino acids (AA) are proposed to help animals combat infection and inflammation. The current study investigates whole-body and splanchnic tissue metabolism in response to a lipopolysaccharide (LPS) challenge with or without a supplement of six AA (cysteine, glutamine, methionine, proline, serine and threonine). Eight sheep were surgically prepared with vascular catheters across the gut and liver. On two occasions, four sheep were infused through the jugular vein for 20 h with either saline or LPS from Escherichia coli (2 ng/kg body weight per min) in a random order, plus saline infused into the mesenteric vein; the other four sheep were treated with saline or LPS plus saline or six AA infused via the jugular vein into the mesenteric vein. Whole-body AA irreversible loss rate (ILR) and tissue protein metabolism were monitored by infusion of [ring-2H2]phenylalanine. LPS increased (P<0·001) ILR (+17 %), total plasma protein synthesis (+14 %) and lymphocyte protein synthesis (+386 %) but decreased albumin synthesis (-53 %, P=0·001), with no effect of AA infusion. Absorption of dietary AA was not reduced by LPS, except for glutamine. LPS increased the hepatic removal of leucine, lysine, glutamine and proline. Absolute hepatic extraction of supplemented AA increased, but, except for glutamine, this was less than the amount infused. This increased net appearance across the splanchnic bed restored arterial concentrations of five AA to, or above, values for the saline-infused period. Infusion of key AA does not appear to alter the acute period of endotoxaemic response, but it may have benefits for the chronic or recovery phases.

Interactions Between Nutrition and Infections With Haemonchus contortus and Related Gastrointestinal Nematodes in Small Ruminants

Interactions between host nutrition and feeding behaviour are central to understanding the pathophysiological consequences of infections of the digestive tract with parasitic nematodes. The manipulation of host nutrition provides useful options to control gastrointestinal nematodes as a component of an integrated strategy. Focussed mainly on the Haemonchus contortus infection model in small ruminants, this chapter (1) illustrates the relationship between quantitative (macro- and micro-nutrients) and qualitative (plant secondary metabolites) aspects of host nutrition and nematode infection, and (2) shows how basic studies aimed at addressing some generic questions can help to provide solutions, despite the considerable diversity of epidemiological situations and breeding systems.

Leucine and methionine deficiency impairs immunity to gastrointestinal parasites during lactation

Lactating rats reinfected with Nippostrongylus brasiliensis fed low-crude protein (CP) foods show reduced lactational performance and less resistance to parasites compared with their high-CP counterparts. Here, we hypothesised that feeding high-CP foods deficient in specific essential amino acids (AA) would result in similar penalties. Second-parity lactating rats, immunised with 1600 N. brasiliensis infective larvae before mating, were fed foods with either 250 (high protein; HP) or 150 (low protein; LP) g CP/kg, or were HP deficient in either leucine (HP-Leu) or methionine (HP-Met). On day 1 of lactation, litter size was standardised at twelve pups. On day 2, dams were either reinfected with 1600 N. brasiliensis larvae or sham-infected with PBS. Dams and litters were weighed daily until either day 8 or 11, when worm burdens, and inflammatory cells and systemic levels of N. brasiliensis-specific Ig isotypes were assessed. Data from five out of sixteen HP-Met rats were omitted due to very high levels of food refusals from parturition onwards. Relative to feeding HP foods, feeding LP, HP-Met and HP-Leu foods reduced dam weight gain and, to a lesser extent, litter weight gain, and increased the number of worm eggs in the colon, indicative of a reduction in resistance to parasites. However, only feeding LP and HP-Leu foods resulted in increased worm numbers, while none of the feeding treatments affected systemic Ig, mast and goblet cells, and eosinophil numbers. The present results support the view that resistance to parasites during lactation may be sensitive to specific essential AA scarcity.

Valine partitioning and kinetics between the gastrointestinal tract and hind limbs in lambs with an adult Trichostrongylus colubriformis burden

Intestinal parasitic infection increases the demand for AA because of increased protein synthesis in the intestine and increased luminal losses of AA, and these increased demands may be supported by increased mobilization of AA from the skeletal muscles. Two experiments were conducted to determine the effects of parasitic infection on valine kinetics within the gastrointestinal tract and hind limbs of lambs fed fresh forages. On d 1, lambs were given 6,000 stage-3 Trichostrongylus colubriformis larvae per day for 6 d (n = 6) or kept as parasite-free controls (n = 6) and fed fresh lucerne (Medicago sativa; Exp. 1) or fresh sulla (Hedysarum coronarium; Exp. 2). On d 48, valine kinetics within the mesenteric- (MDV) and portal-drained viscera (PDV) and hind limbs were obtained by carrying out concurrent infusions of para-amminohippuric acid into the mesenteric vein and indocyanin green into the abdominal aorta (for blood flow), and [3,4-(3)H]valine into the jugular vein and [1-(13)C]valine into the abomasum for 8 h (for kinetics). During the infusions, blood was collected from the mesenteric and portal veins and from the mesenteric artery and vena cava, and plasma was harvested. After the 8-h infusion, lambs were euthanized, ileal digesta were collected, and tissues were sampled from the intestine and muscle (biceps femoris). Tissues, digesta, and plasma were analyzed for valine concentration, specific radioactivity, and isotopic enrichment. In both experiments, intestinal worm burdens on d 48 were greater in parasitized lambs (P = 0.0001 and 0.003). In Exp. 1, parasitic infection increased (P = 0.03) the total valine irreversible loss rate (ILR) in the MDV and PDV. In Exp. 2, luminal ILR of valine in the MDV was reduced (P = 0.01); however, ILR of valine in the PDV was unaffected. Despite these changes within the MDV and PDV, parasitic infection did not affect the ILR of valine within the hind limbs, and valine transport rates were largely unchanged. We suggest that the increased mobilization of AA from the hind limbs that might have occurred in the early phase of inflammation was no longer required when the parasitic infection was established. The MDV and PDV data may indicate that the non-MDV parts of the PDV play an important role in this adaptation, which warrants further study.

Glutamate is the major anaplerotic substrate in the tricarboxylic acid cycle of isolated rumen epithelial and duodenal mucosal cells from beef cattle

In this study, we aimed to determine the contribution of substrates to tricarboxylic acid (TCA) cycle fluxes in rumen epithelial cells (REC) and duodenal mucosal cells (DMC) isolated from Angus bulls (n = 6) fed either a 75% forage (HF) or 75% concentrate (HC) diet. In separate incubations, [(13)C(6)]glucose, [(13)C(5)]glutamate, [(13)C(5)]glutamine, [(13)C(6)]leucine, or [(13)C(5)]valine were added in increasing concentrations to basal media containing SCFA and a complete mixture of amino acids. Lactate, pyruvate, and TCA cycle intermediates were analyzed by GC-MS followed by (13)C-mass isotopomer distribution analysis. Glucose metabolism accounted for 10-19% of lactate flux in REC from HF-fed bulls compared with 27-39% in REC from HC and in DMC from bulls fed both diets (P < 0.05). For both cell types, as concentration increased, an increasing proportion (3-63%) of alpha-ketoglutarate flux derived from glutamate, whereas glutamine contributed <3% (P < 0.05). Although leucine and valine were catabolized to their respective keto-acids, these were not further metabolized to TCA cycle intermediates. Glucose, glutamine, leucine, and valine catabolism by ruminant gastrointestinal tract cells has been previously demonstrated, but in this study, their catabolism via the TCA cycle was limited. Further, although glutamate's contribution to TCA cycle fluxes was considerable, it was apparent that other substrates available in the media also contributed to the maintenance of TCA fluxes. Lastly, the results suggest that diet composition alters glucose, glutamate, and leucine catabolism by the TCA cycle of REC and DMC.

Intestinal amino acid absorption in lambs fed fresh Lucerne ( Medicago sativa) during an established Trichostrongylus colubriformis infection

The effects of an established Trichostrongylus colubriformis infection on amino acid (AA) absorption from the small intestine and their availability to other tissues were determined in lambs 48 days post infection. The lambs were fed fresh Lucerne (Medicago sativa; 800 g dry matter (DM)/day) and dosed with 6000 L3 T. colubriformis larvae for 6 days (n = 5) or kept as parasite free controls (n = 6). Faecal egg production was monitored every second day from day 22 to day 48. A nitrogen (N) balance was conducted on days 35 to 43 after infection, and digesta flow and AA concentration measurements were made on day 44. On day 48 after infection, blood was continuously collected from the mesenteric artery and vein, plasma harvested and AA concentrations measured. Faecal egg production peaked on the 26th day after infection (P < 0.001) and intestinal worm burdens on day 48 were greater (P < 0.001) in the infected lambs. Feed intake and liveweight gain were similar (P > 0.10) between control and infected lambs. Digestibility and flow of DM and N through the digestive tract were also unaffected (P > 0.10) by parasite infection. Despite a trend towards higher abomasal AA flux in the parasitised lambs (P < 0.10), apparent AA absorption from the small intestine and AA availability to other tissues were unaffected (P > 0.10) by infection. These results suggest that an established parasite infection had little effect on the intestinal absorption and availability of AA to other tissues in lambs fed fresh Lucerne.

Six costs of immunity to gastrointestinal nematode infections

The strength of the immune response and the outcome of the interaction of a host with a parasite are influenced by genetic and phenotypic characteristics of both parties, and by environmental variables. Allocation of host resources to immune defence reduces resources available for other life-history traits. This review identifies six potential costs to the host from immune activation. The costs are likely to be broadly applicable to other immune responses in vertebrate species. Five phenotypic costs arise from: (i) increased metabolic activity; (ii) reduced nutrient availability due to anorexia; (iii) altered priorities for nutrient utilization; (iv) change in size and turnover of pools of immune cells and proteins; and (v) immunopathology from inappropriate or excessive immune activation. Subsumed by these costs is the cost of altered efficiency of nutrient use. A sixth cost is the genetic cost which arises from a change in the capacity of offspring to express production and life-history traits following selection for parasite resistance. The sensitivity of immune responses to the phenotypic status of the host, and the role the immune system shares with the neuroendocrine system in controlling use of resources underpin the importance of immunocompetence to the life-history of the host.

Feeding practices and effects of gastrointestinal parasite infections on live weight gain of small ruminants in smallholder mixed farms in Kenya

The objective of this study was to quantify the effects of gastrointestinal nematodosis on live weight gain (LWG) of sheep and goats kept in smallholder farms in Kenya. A total of 307 sheep and goats from smallholder farms were sampled using a 2-stage cluster and systematic random approach. Sampled farms were visited once a month for nine months during which a health and production survey questionnaire was administered, animals weighed and fecal samples taken for fecal egg count. Descriptive statistics and a generalized linear mixed model were performed in SAS. The mean LWG of suckling kids and lambs was low (mean=46 g/day). High fecal egg count and lack of feed supplementation were identified as the main factors limiting growth. Improved helminth control and nutrition are required to optimize production.

Intestinal, hepatic, splanchnic and hindquarter amino acid and metabolite partitioning during an established Trichostrongylus colubriformis infection in the small intestine of lambs fed fresh Sulla (Hedysarum coronarium)

Increased partitioning of amino acids (AA) from skeletal muscle to the intestine and immune system during parasitic infection may be the cause of poor growth in parasitised animals. The effect of an established Trichostrongylus colubriformis infection (6000 L3 T. colubriformis larvae for 6 d (n 5) or kept as parasite-free controls (n 6)) on AA fluxes across the mesenteric-drained viscera, portal-drained viscera (PDV), liver, total splanchnic tissues (TSP) and hindquarters were determined in lambs fed fresh Sulla (Hedysarum coronarium; 800 g DM/d) 48 d post-infection. The lambs were infused with rho-aminohippuric acid (PAH; 723 mg/h) into the mesenteric vein for 8 h to measure TSP plasma flow. Concurrently, indocyanine green (ICG; 14.6 mg/h) was infused into the abdominal aorta to measure plasma flow across the hindquarters. Blood was continuously collected from the mesenteric, portal and hepatic veins, vena cava and the mesenteric artery and plasma harvested. PAH, ICG, AA, metabolite and insulin concentrations were measured. Intestinal worm burdens on day 48 post-infection were higher in the infected lambs (P 0.10). There was a 28 % reduction in the release of AA from the PDV of infected lambs (P < 0.05). The uptakes of most AA were similar in the liver; however, there was increased uptake (P < 0.10) of AA by the TSP of infected lambs. Despite this reduction in AA availability at the liver, there was no effect of parasitic infection on AA uptake across the hindquarters (P < 0.05).

Quantitative aspects of ruminant predicting animal performance

Rations for dairy cattle are currently balanced to meet needs for energy, protein, vitamins, and minerals. While individual vitamins and minerals are considered, energy and protein are generally treated in aggregate even though entities within those aggregates can affect milk yield and composition. Significant efforts have been undertaken to describe ruminal metabolism in detail, but descriptions of post-absorptive metabolism assume constant fractional conversions of energy and protein to milk. A quantitative understanding of nutrient metabolism by the post-absorptive tissues is required, and the splanchnic tissues are critical components of the post-absorptive system as they mediate absorption of nutrients and play a rôle in regulation of metabolite availability.

Glucogenic precursor supply can significantly affect endocrine status as well as splanchnic release of glucose, acetate, lactate, ketones, and the non-essential amino acids. Although the relative affinities of the splanchnic tissues for the essential amino acids (AA) are low as compared with the udder, net clearance on a daily basis represents approximately 2/3 of the net supply to the animal due largely to recycling of AA back to the tissue bed. This could be significantly reduced by stimulating removal and use by the udder as splanchnic affinities are much lower than mammary affinities. Additionally, the essential AA composition of absorbed protein is significantly modified by these tissues due to differing affinities for each of the AA. The extent of that modification is not a fixed constant but rather a function of several factors including milk yield. The accuracy of our current feeding systems could be improved if such variable rates of substrate removal replaced current static estimates.

The effect of concurrent corticosteroid induced immuno-suppression and infection with the intestinal parasite Trichostrongylus colubriformis on food intake and utilization in both immunologically naïve and competent sheep

The nutritional cost of both the acquisition and maintenance of immunity to gastro-intestinal nematodes was investigated using immunologically naïve 5-month-old lambs and immunologically competent 17-month-old ewes. Within each age cohort, animals were either infected with the equivalent of 80 L3Trichostrongylus colubriformislarvae per kg live weight (LW) per day (IF), similarly infected and concurrently immuno-suppressed with weekly injections of 1·3 mg/kg LW of the glucocorticoid methylprednisolone acetate (ISIF), immuno-suppressed only (IS) or remained as controls (C). Body composition of all animals was estimated using X-ray computer tomography on days -14 and 76 relative to the start of infection. Body weight and faecal nematode egg counts (FEC; eggs per gram of fresh faeces (e.p.g.)) were taken weekly and blood samples for serum proteins and antibodies were obtained every 2 weeks. FEC in IF lambs peaked at 1250 e.p.g. before a typical decline as immunity developed to less than 100 e.p.g. by day 75. FEC of less than 100 e.p.g. in IF ewes indicated immunity was maintained. Successful immuno-suppression in ISIF lambs and ewes was indicated by FEC of 4000 e.p.g. on day 75 and was confirmed by comparative worm burdens and serum antibody titres. The typical reduction in voluntary food intake (VFI) as a consequence of infection was observed in IF lambs (proportionately 0·30,P< 0·001) but not in IF ewes, ISIF lambs or ISIF ewes. Gross efficiency of use of metabolizable energy for net energy deposition was reduced by proportionately 0·20 in lambs during acquisition of immunity and by 0·16 in ewes maintaining an established immunity. Infection in immuno-suppressed animals reduced efficiency by 0·05 and 0·15 for lambs and ewes, respectively. These findings allowed the hypothesis that the reduction in VFI and loss in performance in young parasitised sheep is caused by physiological signalling associated with the acquisition phase of the host immune response to infection, rather than simply the damage caused by the parasiteper se.

Catabolism through the threonine dehydrogenase pathway does not account for the high first-pass extraction rate of dietary threonine by the portal drained viscera in pigs

In pigs the extensive threonine utilization by the splanchnic tissues explains the relative inefficiency of dietary threonine conversion for body protein accretion. Two experiments were conducted to estimate the contribution of the portal drained viscera (PDV) and the liver to threonine metabolism and especially catabolism in growing pigs. In the first experiment, four pigs were surgically prepared for chronic catheter insertion in the portal, hepatic and jugular veins and in the carotid artery. They were continuously infused with l-[1-13C]threonine through the jugular catheter. The PDV and total splanchnic viscera (PDV and the liver) extracted 14·3 and 18·8 % of arterial threonine input, respectively. In a second experiment, we studied the metabolism of dietary threonine in the PDV and the liver in six female growing pigs. Animals were surgically prepared as in the first experiment except that l-[1-13C]threonine and [15N]glycine were continuously infused in the duodenum for 10 h. Unlabelled and labelled threonine and glycine PDV, liver and splanchnic tissues balance were calculated from plasma samples taken during the last 2 h of this infusion. Splanchnic tissues extracted 60 % of infused labelled threonine, 88 % of which was extracted by PDV so that threonine extraction by the liver was low. Both the liver and the pancreas can degrade threonine through the l-threonine 3-dehydrogenase pathway but not the intestine. Our data suggest that threonine catabolism through the l-threonine 3-dehydrogenase pathway was only a minor component of total threonine utilization in the splanchnic tissues.

Effect of genetic resistance to gastrointestinal nematodes on plasma concentrations of insulin-like growth factor-1 and leptin in Merino sheep

Gastrointestinal nematode infection in sheep changes the nutritional economy of the host, but little is known about the effects of infection on the hormonal systems that regulate the metabolism of the animal. This study examined two key hormones, insulin-like growth factor-1 (IGF-1) and leptin, in genetically resistant and random bred control Merino sheep in the presence or absence of nematode infection. Sixty-four 10-month-old Rylington Merino wethers, half from the parasite-resistant line and half from unselected control line, were initially maintained at two body conditions (body condition scores averaged 1.7 and 2.5) in individual pens in an animal house. The animals were kept parasite-free for 9 weeks, then ‘trickle-infected’ with Trichostrongylus colubriformis and Teladorsagia circumcincta larvae, each at a rate of 10 000 per week, for 13 weeks. Each body condition score group was subdivided into two groups at the beginning of the infection procedure and feed supply was controlled at 1× or 1.5× the maintenance metabolisable energy requirement. Plasma IGF-1 concentrations decreased marginally by day 21 of infection, then markedly by day 49, and then remained low until day 84. Plasma leptin concentrations tended to increase during the infection period. Both body condition and feed intake had significant effects on IGF-1 and leptin concentrations, and the higher concentrations were related to the good body condition or high feed intake. The parasite-resistant sheep had consistently higher concentrations of IGF-1 compared with the controls, whereas the concentrations of leptin were similar. The significant changes in IGF-1 but not leptin suggest that infection may have a more significant impact on protein anabolism, and least impact on lipid metabolism. Selection for parasite resistance appears to result in enhanced protein anabolism.

A model for predicting feed intake of growing animals during exposure to pathogens

A general model is proposed for predicting the effects of subclinical pathogen challenges of different doses and virulence on the relative feed intake (RFI) of animals. The RFI is defined as the feed intake (FI, kg/d) of the animal challenged by a pathogen divided by its FI in the same state had it not been challenged. Actual FI can be predicted from the RFI and the animal's state. The RFI was assumed to be affected only when animals were naïve to a particular pathogen (i.e., had not previously experienced it) and when the challenge dose was above a predetermined threshold. The model is for the period from recognition of a pathogen through acquisition and subsequent expression of immunity. The way in which RFI changes with time is described by 5 main parameters and is based on data for RFI during different pathogen challenges of a range of hosts. Lag time (L, d) is the delay from a pathogen challenge until any effects on RFI are seen. Reduction time (R, d) describes the time it takes for the lowest value of RFI (lambda) to be achieved. The duration time (D, d) describes the time that lambda is maintained for, and rho (RFI/d) describes the rate of recovery of RFI until RFI = 1. There is no compensatory intake, and RFI is always < or = 1. The effects of host resistance on the values of the model parameters are proposed. Attempts were made to parameterize the model; when data were scarce, initial parameter values were derived on conceptual grounds. Predictions of the effects of pathogen dose, virulence, and host resistance are described and discussed. When comparing the responses in RFI for different genotypes, it is crucial to define the pathogen challenge (in terms of dose and virulence) and the degree of resistance of different hosts. Possible interactions between dose, virulence, and resistance were explored. Feed intake of healthy and challenged animals, at a time, may be different once the challenged animal has recovered (RFI = 1). The issue of reductions in FI during pathogen challenges is important for nutritionist and animal breeders. The large variation that has been observed for reductions in FI during pathogen challenges may be a viable point of selection. The points highlighted will aid selection strategies by quantifying the effects of pathogen dose and virulence, and time, on the FI of challenged animals. The proposed model may be integrated with other models of growth to predict animal performance during exposure to pathogens.

Intestinal protein supply alters amino acid, but not glucose, metabolism by the sheep gastrointestinal tract

This study was intended to establish the extent which amino acids (AAs) and glucose are net metabolized by the gastrointestinal tract (GIT) of ruminant sheep when intestinal protein supply is varied. Wether sheep (n = 4, 33 +/- 2.0 kg) were fitted with catheters for measurement of net absorption by the mesenteric (MDV) and portal-drained (PDV) viscera and a catheter inserted into the duodenum for casein infusions. Sheep received a fixed amount of a basal diet that provided adequate metabolizable energy (10.9 MJ/d) but inadequate metabolizable protein (75 g/d) to support 300-g gain per day. Four levels of casein infusion [0 (water), 35, 70, and 105 g/d], each infused for 5.5 d, were assigned to sheep according to a 4 x 4 Latin square design. [methyl-(2)H(3)]leucine was infused (8 h) into the duodenum while [1-(13)C]leucine plus [6-(2)H(2)]glucose were infused (8 h) into a jugular vein. With the exception of glutamate and glutamine, net absorption of AAs increased linearly (P < 0.05, R(2) = 0.46-1.79 for MDV; P < 0.05, R(2) = 0.6-1.58 for PDV) with casein infusion rate. Net absorption by the PDV accounted for <100% of the additional supplies of leucine, valine, and isoleucine (0.6-0.66, P < 0.05) from casein infusion, whereas net absorption by the MDV accounted for 100% of the additional essential AA supply. Glucose absorption (negative) and utilization of arterial glucose supply by the GIT remained unchanged. There was a positive linear (P < 0.05) relation between transfer of plasma urea to the GIT and arterial urea concentration (MDV, P < 0.05, r = 0.90; PDV, P < 0.05, r = 0.93). The ruminant GIT appears to metabolize increasing amounts of the branched-chain AAs and certain nonessential AAs when the intestinal supply of protein is increased.

The effect of providing feed supplementation and anthelmintic to donkeys during late pregnancy and lactation on live weight and survival of dams and their foals in central Ethiopia

Anthelmintic treatment (A), feed supplementation (F), anthelmintic and feed supplementation (A+F) or traditional management (Control) was given to 166 pregnant female donkeys in three localities (Holetta, Debre Zeit and Adami Tulu) in Ethiopia during an on-farm study. Treatments started during the last trimester of pregnancy and continued until 6 months after parturition when the foals were weaned. The same treatments were administered to foals once they reached 1 month of age. Live weights of adults and foals were measured throughout the study along with work output of adult donkeys and survival to weaning of the foals. Faecal worm egg counts (FEC) and blood packed cell volumes (PCV) were recorded monthly. When applied alone, anthelmintic treatment (A) or feed supplementation (F) had no significant effect on live weight gain or foal survival. However, when combined, anthelmintic and feed supplementation (A+F) significantly (p<0.05) improved both live weight gain in adults and foals and foal survival. Workout was not affected by any of the treatments. Treatments A and A+F resulted in a highly significant (p<0.001) reduction in FEC in all three localities during the course of study and for at least 6 months after the last dose of anthelmintic in one of the study areas (Holetta). None of the treatments had any significant effect on PCV. Donkey owners in Ethiopia should be encouraged to adopt both anthelmintic treatment and feed supplementation if they expect tangible benefits in animal performance.

Interactions between nutrition and gastrointestinal parasitism in sheep

Effects of gastrointestinal nematode infection on metabolism and nutrient utilisation in sheep are reviewed. Infection induces protein deficiency by increasing the demand for amino acids in the alimentary tract while reducing supply through depression of appetite. Mechanisms through which improved protein nutrition could improve the performance of the host are then discussed. Opportunities for capitalising on such effects are limited by our rudimentary understanding of the cell-mediated immune response in gastrointestinal epithelial tissue. Both resistance of the animal to larval establishment and performance in the face of larval challenge can be enhanced by improved protein nutrition. However, enhanced immune responses may not necessarily be synonymous with improved productivity except at luxurious levels of protein intake, because of apparently competing demands for protein. Such levels of protein nutrition are difficult to achieve in pasture-based systems, because of the protein limiting role of the rumen. Work with proteinprotecting tannins to overcome this limitation is discussed. The much more limited evidence for effect of mineral nutrition, particularly copper (Cu), molybdenum (Mo), cobalt (Co) and phosphorus (P), on outcome of larval challenge is also reviewed.

Animal models of amino acid metabolism: a focus on the intestine

One important advantage of animal models is that they permit invasive approaches and can be especially valuable when evaluating tissue and specific features of metabolism in situ. The focus of this presentation is current models, which are providing insights into the pivotal importance of the gastrointestinal tract in amino acid metabolism. Intestinal amino acid metabolism is conceptually and technically difficult to approach and multiple processes must be accounted for: protein synthesis and degradation; transit of amino acids in both directions across the basolateral surface of enterocytes, in addition to uptake on the apical side; arterio-portal differences as well as net portal appearance during uptake of defined amino acid mixtures appearing on the luminal side; first pass amino acid metabolism. These key features are largely impossible to study without access to invasive approaches in vivo and cannot be reproduced in vitro. Douglas Burrin, Ron Ball, and Vickie Baracos and their co-workers have used the domestic piglet to study intestinal protein metabolism in situ in three distinctly different and complementary approaches. Collectively, their approaches allow a means to describe the key elements of intestinal amino acid capture (and release) and the means to probe their physiological and pathological variation. It seems evident that the portal-drained viscera represent sites of quantitatively important amino acid catabolism, and that this capacity combined with hepatic metabolism would largely limit the possibility of toxic sequelae of amino acids taken orally.

Digestion and nutrient net fluxes across the rumen, and the mesenteric- and portal-drained viscera in sheep fed with fresh forage twice daily: net balance and dynamic aspects

Digestion and portal net flux of nutrients were studied in sheep fed twice daily with fresh orchard-grass. Digestive flows were measured in six fistulated sheep using the double-marker technique. Three sheep were fitted with catheters and blood-flow probes, allowing nutrient net flux measurements across the portal-drained viscera (PDV), the mesenteric-drained viscera (MDV) and the rumen. Total tract apparent digestion of N was similar to portal net appearance of N, calculated as the sum of free amino acids (FAA), peptide amino acids (PAA), NH3, and urea net fluxes. PAA accounted for 25 % of non-protein amino acid net release across the PDV. With the exception of glycine and glutamate, the small intestine was the main contributor to this PAA net release. The essential amino acid (EAA) apparent disappearance between the duodenum and the ileum was lower than the net appearance of EAA (FAA + PAA) across the MDV. The value of PDV:MDV flux of free EAA was, on average, 78 %. The rumen accounted for 30 % of the net uptake of EAA by the PDV tissues not drained by the mesenteric vein. Rumen net release of acetate, propionate, butyrate, 3-hydroxybutyrate, and lactate accounted for 70, 55, 46, 77 and 52 %, respectively, of their portal net releases. Conversely, the small intestine was a net consumer of arterial acetate and 3-hydroxybutyrate. Dynamic study of nutrient net fluxes across the PDV showed that throughout a feeding cycle, the liver faced a constant flux of amino acids (AA), whereas volatile fatty acid and NH3 net fluxes varied in response to the meal. The present study specified, in forage-fed sheep, the partitioning of nutrient net fluxes across the PDV and the role of peptides in portal net release of AA.

Oxidation of essential amino acids by the ovine gastrointestinal tract

It is not known if the ruminant animal gastrointestinal tract (GIT) can oxidise essential amino acids (AA) other than leucine. Therefore, the oxidation of four essential AA (leucine, lysine, methionine and phenylalanine), supplied systemically as labelled 1-13C forms, was monitored across the mesenteric-drained viscera (MDV; small intestine) and portal-drained viscera (PDV; total GIT), as part of a Latin square design, in four wether sheep (35-45 kg) fed at 1.4 x maintenance. Oxidation was assessed primarily by appearance of 13CO2, corrected for sequestration of [13C]bicarbonate. The GIT contributed 25 % (P<0.001) and 10 % (P<0.05) towards whole-body AA oxidation for leucine and methionine respectively. This reduced net appearance across the PDV by 23 and 11 % respectively. The contribution of MDV metabolism to total PDV oxidation was 40 % for leucine and 60 % for methionine. There was no catabolism of systemic lysine or phenylalanine across the GIT. Production and exchange of secondary metabolites (e.g. 4-methyl-2-oxo-pentanoate, homocysteine, 2-aminoadipate) across the GIT was also limited. Less AA appeared across the PDV than MDV (P<0.001), indicative of use by tissues such as the forestomach, large intestine, spleen and pancreas. The PDV: MDV net appearance ratios varied (P<0.001) between AA, e.g. phenylalanine (0.81), lysine (0.71), methionine (0.67), leucine (0.56), histidine (0.71), threonine (0.63) and tryptophan (0.48). These differences probably reflect incomplete re-absorption of endogenous secretions and, together with the varied oxidative losses measured, will alter the pattern of AA net supply to the rest of the animal.

Effect of dietary fiber on endogenous nitrogen flows in lactating dairy cows

The effect of dietary fiber on endogenous N secretion was studied using a 15N isotope dilution technique in four fistulated Holstein cows. Two isonitrogenous diets differing only in fiber (NDF and ADF) content were used in a crossover design. One diet (HF) contained 37.4% NDF, while the other (LF) contained 23.3%. A new model was developed to estimate endogenous N secretions and losses for the preintestinal, intestinal, and the total sections of the gastrointestinal tract. Three precursor pools: TCA-soluble fraction of plasma, intestinal mucosa, and milk were compared. Although endogenous losses estimated with the model were numerically different for each precursor pool selected (TCA-soluble fraction > mucosa > milk), treatment effects were similar. As intestinal mucosa is probably closest to the precursor pool, these data are discussed. Non-urea N endogenous secretions contributed 13% of the duodenal N flow but were not affected by the fiber content of the diet. The nonurea N endogenous flow at the duodenum was comprised of approximately equal inputs from endogenous N direct, and that incorporated into the microbial biomass. Total endogenous N flows at the duodenum exceeded, by nearly twofold, estimated inputs of urea-N to microbial biomass. Metabolic fecal output averaged 17% of fecal N and was not affected by level of dietary fiber, but net losses from secretions occurring in the small intestine were higher with the low fiber diet. Overall, endogenous N secretions represented 30% of total digestive tract protein synthesis.

Effect of supply of metabolizable protein on whole body and splanchnic leucine metabolism in lactating dairy cows

The effect of the supply of metabolizable protein (MP) on protein metabolism across the splanchnic tissues was determined in six catheterized lactating Holstein cows. In a crossover design, two isonitrogenous (16.3% CP) diets balanced to provide a low (Lo-MP) or high (Hi-MP) supply of MP were fed over 35-d periods. After 24 d of feeding, N balance was determined over a 6-d period. On d 33, [13C] sodium bicarbonate was infused into one jugular vein for 6 h, and hourly breath samples were collected. On d 34 or 35, L[1-(13)C] leucine was infused into one jugular vein, and between 2 to 6 h of infusion, breath and blood samples were taken hourly from the portal and hepatic veins and an artery. Isotopic enrichments of plasma leucine, 4-methyl-2-oxopentanoate, and expired CO2 were determined for calculation of leucine kinetics. Net leucine absorption was greater, either on a direct basis (leucine transfer only) or corrected for portal-drained viscera metabolism to 4-methyl-2-oxopentanoate and CO2 for the Hi-MP diet. There were no effects of diet on hepatic net flux of leucine across the liver, and, thus, more leucine was available to peripheral tissues with the Hi-MP diet. Combined with an increment in portal absorption of most of essential AA, this led to increased milk protein output, although it only represented 16% of the additional available leucine. Whole body leucine oxidation was also greater for the Hi-MP diet, as was leucine used for protein synthesis. Despite these changes, MP supply did not affect irreversible loss rate of leucine by portal-drained viscera and the liver; these averaged 35 and 20% of whole body irreversible loss rate, respectively. These ratios confirm the high metabolic activity of splanchnic tissues in lactating dairy cows, which are even greater than previously reported in growing ruminants.

Nutrient partitioning between reproductive and immune functions in animals

The physiological processes that underlie the reproductive cycle impose considerable metabolisable protein (MP) demands on a female, especially during the periparturient period. When MP supply falls short of MP demand (i.e. MP becomes scarce), certain, if not all, bodily functions are expected to be penalised. It has been proposed that partitioning of scarce MP is prioritised to reproductive rather than to immune functions. In other words, at times of MP scarcity, the penalty on expression of immunity would be expected to be greater than that on reproduction. This hypothesis forms a nutritional basis for the occurrence of periparturient breakdown of immunity to parasites (BIP), which can be observed in many host-parasite systems. In the present review we explore this nutritional basis, using periparturient sheep infected with the abomasal nematode Teladorsagia circumcincta as an example, and attempt to quantify its occurrence. Evidence supporting the nutritional basis of periparturient BIP is reviewed, covering experiments in which nutrient supply (from both exogenous and endogenous sources) and/or nutrient demand were manipulated. Quantitatively, MP requirements for expression of immunity to T. circumcincta were estimated to be about 1 g/kg metabolic body weight (body weight 0.75) per d, approximately 5% of the maximum MP requirements of periparturient sheep. The major component of this requirement was assumed to be for replenishing irreversible plasma protein losses into the gastrointestinal tract. Although confirmation of this estimate is required, such estimates may be used to improve the known MP requirements of periparturient animals, enabling the extent and the consequences of periparturient BIP to be minimised.